1. Field
Exemplary embodiments of the present invention relate to a high efficiency light emitting diode and, more particularly, to a high efficiency light emitting diode having improved light extraction efficiency and a method of fabricating the same.
2. Discussion of the Background
A light emitting diode is a semiconductor device that emits light by recombination of electrons and holes in a junction between a P-type semiconductor and an N-type semiconductor. Particularly, a light emitting diode using group III-V based semiconductors such as gallium nitride (GaN) has a direct transition-type energy band structure and may have high internal quantum efficiency. Among group III-V based semiconductors, a gallium nitride semiconductor has attracted attention as a material for light emitting diodes.
Luminous efficiency of light emitting diodes is generally determined by internal quantum efficiency and light extraction efficiency. Light extraction efficiency means a ratio of photons emitted outside of a light emitting diode, that is, a free space, to photons emitted from an active layer. When the light emitting diode has low light extraction efficiency, the number of photons escaping to the free space is low even when the light emitting diode has high internal quantum efficiency. As a result, a light emitting diode having low light extraction efficiency exhibits low efficiency as an actual light source.
Light extraction efficiency is decreased by total internal reflection due to a difference in index of refraction between the light emitting diode and free space. Due to such total internal reflection, photons generated in the active layer are extinguished inside the light emitting diode instead of escaping to the outside of the light emitting diode.
In order to reduce optical loss due to total internal reflection, various techniques have been developed. For example, surface roughness of the light emitting diode may be increased to reduce total internal reflection at the surface of the light emitting diode. In particular, increased density of surface roughness may further reduce total internal reflection. To increase surface roughness of the light emitting diode, dry etching or wet etching may be used.
It may be difficult to provide relatively dense surface roughness using dry etching due to a limit in photolithography, and wet etching may be used instead. However, when the light emitting diode has a stable surface, it may be difficult to increase surface roughness via wet etching. For example, an N-face surface may be more stable than a Ga-face surface in a gallium nitride-based semiconductor, so it may be difficult to increase the surface roughness of the N-face surface of the light emitting diode by wet etching.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form any part of the prior art nor what the prior art may suggest to a person of ordinary skill in the art.